Power Mirror System Explained

For a visual reference, refer to Robert Bentley manual page 97.184 for the circuit diagram of this system. It is a good idea to have it open to that page when reading this article.

Driver’s side:
There are only two wires that run from the fuse box/chassis through the rubber boot into the driver’s side door for mirror MOVEMENT. The power wire (black/yellow) from pin G1 of the fuse box (12V with ignition switch ON) goes straight to the mirror control switch in the driver’s door. A ground wire (brown) plugs into the pin on the grounding ring above the fuse box, and goes straight to the driver’s side mirror. At the mirror, the ground wire splits in two and also provides ground for the defroster in the glass. Power for the defroster (white/green) does not go through the switch but straight to the mirror glass for defrost. That circuit is powered by the rear window defroster switch. Mirror defrost comes on whenever the rear window defrost is switched on.

Three power wires run from the mirror switch to the mirror: black, blue, and white. The power for up/down and left/right are the same two wires, the black and blue ones. The mirror switch just reverses polarity for reverse direction. There is only ONE motor in the mirror, it makes a whirling sound when operating. The additional white positive wire from the switch operates a solenoid in the mirror that makes it change axis from left/right to up/down. This is the clicking sound you hear. Whenever you move the switch for up/down motion the white wire goes hot or "ON." This powers the solenoid which changes the mirror movement from in/out to up/down. It stays cold or "OFF" when operating the mirror left/right. So:

• No power to white wire: mirror moves in/out only, whirling sound, no clicking sound.

• Power to white wire: mirror moves up/down, whirling sound AND clicking sound.

All of the wires we have discussed to this point are part of the driver’s side mirror harness, harness #1.

Passenger side:
Three power wires that are part of harness #1 run to the passenger mirror from the mirror switch in the driver’s door. They are blue/black, black, and white. They run through the rubber boot on the driver’s side door jamb and out under the dash near the fuse box. There they plug into the under-dash harness (#2) in which there is an additional brown ground wire for the passenger side mirror. That wire also grounds on the same ground ring above the fuse box. Harness #2 runs all the way across the vehicle under the dash and plugs into harness #3 behind the glove box. Harness #3 runs through the rubber boot on the passenger door jamb and into the passenger door. The passenger side mirror is identical to the driver side mirror in terms of function and how it is wired. It has one motor and one solenoid, three wires operate it, and the defrost wires have nothing to with the motion, at all.

The whole system:
What is unusual about this system and throws people for a loop is that the black and white wires are COMMON to both mirrors. The black wire may be positive 12V or ground at any given time depending on switch position, up/down, left/right. This will be so at BOTH mirrors simultaneously. But only ONE mirror, the one selected by rotating the switch to “L” or “R,” will get positive 12V or ground on the BLUE or BLUE/BLACK wire, left and right mirror, respectively.

That is not the most confusing part. Anytime EITHER mirror is moved up/down, BOTH mirrors get power to the solenoid via the white wire. So, both solenoids make a clicking sound—even the one in the mirror that IS NOT selected and being controlled. That is a crummy thing about this system. I think both solenoids being powered creates a bit of a power drain in the system, and one reason these systems commonly need higher-than-usual power to operate. Even when all is perfect, it is not unusual for the system to require more than 12V to operate well (engine running and revved up). That is why on some vehicles the mirrors work fine when driving down the road, but not when sitting still with the engine not running.

Basic troubleshooting rules of thumb based on logic and our experience:

1) Before you mess around with anything, start the engine and rev it up to 2000 rpm and see if things work. If they do, don’t mess with anything, it is what it is!

2) If neither mirror works at all, no sounds at all, the problem is probably no power getting to the system, at all. That is likely a wiring issue, usually a broken wire(s) in the driver’s side door jam. It is a crummy, tedious job to get to these wires—so, take a deep breath and bust out some tools.

3) If one mirror works fine but the other does not—it is probably the switch. Often just taking it apart and giving it a thorough cleaning is all that is needed.

4) If both mirrors work but only in the in/out (no up/down)-it is most likely the switch. This is because the white wire between the switch and driver’s side mirror runs directly from the switch to the mirror, not door jam cycling involved to break a wire.

5) If only the passenger side mirror has no up/down motion—that is probably a broken white wire in one of the door jams.

6) If only one mirror is acting up, it could be the motor/solenoid assembly. They are the same left/right, so you could try swapping them before buying a new on.

Have fun with your mirrors!